Decadal Variability

The North Pacific Climate system exhibits fluctuations on decadal and multidecadal time scales. One hypothesis is that part of this variability is caused by the excitation of Rossby basin modes in the ocean (Cessi & Primeau 2001). Such a modal origin would be important for predictability of the Pacific Decadal Variability (PDV).

In the first phase of this project we tried to find support for this hypothesis in a state-of-the-art coupled climate system model, the CCSM3 (Weijer et al. 2013). Using statistical techniques like Empirical Orthogonal Function (EOF) and Principal Oscillation Pattern (POP) analysis we showed that the dominant 25-yr variability of sea surface temperature (SST) variability is unlikely to be related to an oscillatory ocean mode. However, some secondary peaks of enhanced energy at 17 and 8.5 yr seemed to be associated with internal ocean dynamics. However this variability of the subsurface pressure field does not display the characteristics of classical Rossby basin modes.

In the second phase of this project, I am collaborating with Niklas Schneider (U. Hawaii) to examine the origin of these spectral peaks in eastern boundary pressure of 17 and 8.5 yr.